Does my mother in law have rights to her rental property?

Husband & I are on the mortgage of the home, We signed for her in 2007. she pays the mortgage and taxes. she has missed several mortgage payments, property tax payments. We've paid those for her. what can she do to us? she is trying to claim equitable rights to the property, hired an atty, threatening to go to 'litigation'. Atty letter doesn't say why we're going to litigation, just that mother in law is asserting equitable rights.